lewis



L. V. LEWIS.

RAILWAY SIGNALING. APPLICATION FILED FEB. 26. 1921.

Reissued Apr. 26, 1921 15,096.

5 SHEETS-SHEET L ATTORNEY L. v. LEWIS. RAILWAY-SIGNALING.

APPLICATION FILED FEB. 26,1921. I Reissued Apr. 26, 1921. 15,096.

5 SHEETS-SHEET 2.

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' B aaz-rnmu N-L AfToRNEY LUV. LEWIS.

RAILWAY SIGNALING. APPLICATION FI'LED rss. 26. I921.

Reissugd Apt-26, 1921.

PROCEED CURRENT IN (b) POTENTIAL BETWEENW:

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CAUTION WWW-W INVENTOR:

7 am-rwm M. ATTORNEY L. v. LEWIS.

RAILWAY SIGNALING.

APPLICATION FILED FEB. 26. 1-921.

15,096. 5 SHEETS-SHEET 4.

Beissued Apr. 26, 1921.

I INVENTORZ Kerr BY a az N ATTORNEY mW Lu 0W dI I. 1 F NV g NV an 3 on 2mQw I mQn 4 SH w I I INF i m E I L IPA-3. \Lv fisa F E. 2L PW:

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. APPLICATloN FILED FEB. 25, I92- Beissued Apr. 26, 1921. 15 ,096.

5 SHEETS-SHEET 5.

INVENTOR 0L fa-1W M1. ATTORNEY in" is a specification.

UNITED STATES PATENT OFFICE.

LLOYD V. LEWIS, OF EDGEWOOD BOROUGH, PENNSYLVANIA, ASSIGNOR TO THE UNIONSWITCH & SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIAA COR- PORATION OFPENNSYLVANIA.

RAILWAY SIGNALING.

Specification of Reissued Letters Patent. Reis ed A 26 1921 Original No.1,365,329, dated Ian-nary 11, 1921, Serial No. 121,378, filed September21, 1916. Application for reissue filed February 26, 1921.

Be it known that I, LLOYD V. Lnwrs, a citizen of the United States,residin Edgewood borough, in the county of 11agheny and State of Pennslvania, have invented certain new and use ul Improvements in RailwaySignaling, of which the follow- My invention relates to railwaysignaling, and particularly to signaling of the type in which highfrequency oscillating currents are employed to control either fixedsignals located along the trackway, or signals carried on the railwayvehicles, or both.

I will describe. certain forms of signaling systems and apparatusembodying my in vention, and will'then point out the novel featuresthereof in claims.

- In the accompanying drawings, Figure 1, which is shown'in two parts Aand B respectively, is a diagrammatic view showing one form of signalingsystem embodying my invention; Fig. 2 1s a diagrammatic vlew showlng amodified arrangement of the vehicle-carried receiving circuit shown inFig.

1. Fig. 3 is a diagrammatic view showing one form of speed governingapparatus which may be employed in conjunction with the relays shown onthe vehicle in Fig. 1. Fig. 4 is a group of diagrams illustrating thecurrent and voltage waves in certain parts of the vehicle-carriedapparatus shown in Fig. 1. Fig. 5 is a view showinga modification of thesystem shown in Fig. l and embodying my invention. Fig. 6 is adiagrammatic view showing a modified arrangement of vehicle-carriedapparatus of that shown in Similar reference characters refer to similarparts in each of the several views.

Referring first to Fig. 1, the reference characters Hand H" designatethe track rails of a railway over which traffic normally moves in thedirection indicated by the arrow, which rails are divided into blocksections A-B, B-C, C-D, etc., by insulated joints 2, 2, etc. As hereshown. both rails are divided by such joints, and inductive bonds 3 and3 connected at their middle 60 points by conductors 4 are provided tocon- Serial No. 448,224.

duct the propulsion currentv around these o1nts when the propulsionenergy for the cars or trains is electricity. It is immaterial, however,to the present invention how the segregation of the block sections isaccomphshed, and whether or not the propulsion energy is electricity.and if it is whether it is direct or alternating current. i

For each block section I provide means for impressing upon the railsthereof alternating signaling currents differing in frequency, whichcurrents are preferably of a'hi h frequency, and which currents differin frequency preferably by a small value. Consequently when thesecurrents are both supplied to the rails of any one block section therewill be in said rails a resultant current of beat frequency, tha t is, acurrent of periodically varying amplitude, the pe-riodifor each blocksection are generated locally by two similar sets of appartus, one ofwhich is connected at all times to the track rails and cou'iprises avacuum tube or bulb K containing a filament 6, preferably of tungsten, ametallic plate 8, and a metallic grid 7 located between the filament andthe plate. The filament 6 is constantly heated by a battery 9. A secondbattery 10 is included in a circllit comprising a transformer winding12, filament 6, and plate 8. Across the terminals of transformer Winding12 is connected a tuned circuit comprising condenser 13 and a winding 11of a transformer of which the rail bond 3 forms the secondary.

Oscillating currents are set up and maintained in this circuit, and soare impressed on the track rails. the frequency of which currentsdepends on the tuning of a closed resonant circuit comprisingtransformer secondary 14 and condenser 15. 'The terminals of condenserare connected respectively to filament 6 and grid 7.

The oscillating difference of potential across condenser 15 is therebyimpressed between filament 6 and grid 7 to produce correspondingvariations in the current in the and the secondary of which is connectedcircuit of. battery 10, resulting in the pro ducton of oscillations inthe resonant circuit comprlslng condenser 13 and winding 11 of bond 3vwhereby the oscillations are impressed upon the track rails.

The second set of generating apparatus, comprising bulb K',battery 10,et'c., and which is tuned to a frequencylower than that of the first setis controlled by a con tact 18 of a relay It whichrelayis in turncontrolled by traffic conditions in the sectlon next in advance ashereinafter explained.

The result is that the rails of any one block section are alwayssupplied with signaling current of the higher frequency, and are alsosuppliedwith current of thelower frequency when the section next inadvance is unoccupied and the rails thereof are intact.

Although I have herein shown means for generating the two signalingcurrents locally for each section, it is understood that'any othersuitable means may be employed for supplying these currents to therails.

Located adjacent the entrance end of each block section are two relays Rand R, the

former of which is responsive to the signala ing current of higherfrequency and'the latthe component signaling currents alone.

These relays are energized as follows: The

" i rail bond 3 constitutes'the primary of a.

' vice K hereinbefore described:

I transformer of which 19 is the secondary winding, and this secondaryis included in a circuit 1) comprising transformer primary 16 andcondenser 20, which is tuned broadly to the mean of the two componentsignaling current frequencies. Connected across the terminals ofcondenser 20 is a circuit including a condenser 23 shunted by a highresistance 24, and the grid and filament of a vacuum tube device K",similar to the dc- Sustained osclllations in the circuit 1) will producean oscillating difference of .potential on con denser 20 which, due tothe rectifying ac- 1 permit the charge on condenser 23 to leak tion ofthe tube, will gradually build up a charge on condenser 23 andconsequently onthe grid 7R, resulting in a decrease in the steady valueofthe current from a battery 10 in the plate circuit of the tube. creasein the oscillations in circuit 2) will off through resistance 24,thereby permitting "an increase in the current from battery 10".

Eachgroup of oscillations in circuit b, there fore, produces a singlefluctuation of the battery current in circuit cl, that is, there will bea single fluctuation of the current in cir- .ter to the beat frequencybut not to either of cuit d for e ch beat or periodic variation in theamplitude of the signaling currents. Relay R is supplied withalternating current of. a frequency corresponding to this beat frequencyby a transformer 28 the primary.of which is included 'in circuit d withthe relay;this.relay is designed torespond to current of. the frequencywhich it thus receives, but not. to the frequency of either of thecomponent signaling currents. Coupled to transformer coil 16incircuit 1) is a secondary coil 22 in a circuit 0 tuned by means ofcondenser 21 to resonance at the frequency of the higher frequencysignaling current. Connected across the terminals of condenser 21 is .acircuit including the grid 7 and filament 6 of bulb I The plate circuitof bulb Kf' includes filament 6, battery 10 and primary of transformer27, (which is tuned by means of condenser 26) and plate 8. Sustainedoscillations in resonant circuit 0 will produce an oscillatingdifl'erenceof potential between filament 6and grid 7 which will producecorre- 'sponding variations in the current in the" circuit of battery 10which will be repro-' duced as oscillations in the tuned circuit comrising secondary of transformer 27,

con enser 25 and relay R. Relay B, therej fore, receives oscillatingcurrent corresponding in frequency to the higher frequency componentcurrent. This relay is designed to respond to such current. p I

As hereinbefore pointed out, the supply ofthe lower frequency signalingcurrent to each section is controlledby a contact 18 of relay R for thesection next in advance, which contact is closed only when the sectionin advance is'unoccupied. 'It will be evident, therefore, that the railsof a section immediately in 'the rear of an occupied section containcurrent of the higher signal-. ing frequency only, whereasthe rails ofthe second section in the rear of an occupied section contain signalingcurrent of both frequencies. It follows. therefore, that for the sectionin the rear of an occupied section relay R is energized and relay Rde'e'nergized, but for the second section in the rear of the occupiedsection both relays R and R are energized. I y

In Fig; 1 I have shown fixed or roadside signals F. F, etc., buttheprovision of such signals is not essential in all cases for thereason that the passage of cars or trains along the railway may beadequatelygoverned by the signals and other apparatus on the cars ortrains themselves as {hereinaften described and explained. As: (shown inFig. 1, one fixed signal F is located adjacent I the entrance end ofeach block section and as here shown each of these signals is of thewell' known light type, comprising three electric lamps G, Y and R,indicating low and red glasses in front of t e respective lamps, as iswell understood in the art.

The three lamps of each signal are con-v trolled by the adjacent relays'R and B through the 'medium of circuits supplied with current from asuitagle source, such as a battery 50. These circuits need-not be tracedin detail, it bein sufficient to oint out their operations brie y asfollows: amp G. is controlled by the upper contact point 29 of relay Rand the upper contact point 46 of relay R, so that this lamp can beilluminated only when both relays are energized, that is, when thecorresponding block section and the section next in advance areunoccupied; lamp Y is controlled b the upper contact point 29 of relay Ran the lower contact point 46 of relay B, so that this lamp isilluminated onl when relay R is energized an relay denergized,

,that is, when the orresponding block. sec-.

tion is unoccupied and the section next in advance is occupied; lamp Ris controlled only by the lower contact point 29 of relay. R so thatthis lamp is lluminated only w en this rela is deenergized, thatis, whenthe correspon ing section isoccupied by a car or train. The conditionsof. the roadside signal apparatus by virtue of which the signals arecaused to indicate proceed, caution and stop are shown respectively atlocations B, C and D. in Fig. 1, the cau-,,

tion and stop indications at locations C and D being due to the presenceof a vehicle V in section D-E.

At the left hand end of Fig. 1, part A, I have showndiagrammatically arailway-vehicle V (a car, locomotive or train) which is equipped withapparatus adapted to be aling currents in the control ed by the s1 7track rails and whic apparatus is arranged to give signal indications byvirtue of which. the speet and progress of the vehicle are governed. Ashere shown, the signaling apparatus comprises three lamps G, Y and whichlamps are used to give the same indications as those in the roadsidesignals, that is, roceed, caution and stop. The signa lamps on thevehicle are controlled by two relays P and P in exactlv the same manner,as the lamps in each roa side signal F are controlled by thecorrespondin relays R and R. Mounted on the vehicle in front of theforward pair of wheels is a coil 30, which is in inductive relation toboth of the track rails in advance of the forward axle. This coil isincluded in a circuit 'a tuned broadly to the P and P" is identical .tothe apparatus in in resonant circuit a.

thetrackwa between circuit 6 and relay R, except t at relay P is adirect current relay and is connected directly into the circuit ofbattery 10 and is adjusted to repond to an increase in the current ofbattery 10* due to the presence of'oscillations Suflice it to say thatrelay P is responsive to the signaling current of the high frequency andrelay P is res nsive to the beat frequency.

he operation of the vehicle-carried aparatus-will be readily understoodfrom the ollowin brief explanation. Sections AB and B being bothunoccupied except for vehicle V both relays P and P on this vehicle areenergized so that the green lamp. G is illuminated indicatin proceed. Asthe vehicle enters section %3-C no change will occur because thissection and the section -C-D in advance are unoccupied. When, however,the vehicle enters section CD, which is the section in the rear of anoccupied section, relay P will become deenergized because thesignalingcurrent of lower frequency is absent; lamp G will thereforebecome extinguished and lamp Y will become illuminated, so that thesignal on the vehicle indicates caution. As the vehicle enters sectionI)E, which is already occupied, relay P will also become deenergiz edbecause of the absence of signaling current in the rails of thissection, so that lamp Y will become extinguished and lamp R will beilluminated, indicating stop.

In Fig. 2 I have shown an alternative means for transmitting energy fromthe track rails to the apparatus on the vehicle. In this view, the coil30 of Fig. 1 is eliminated, and the resonant circuit a, 'whichcorresponds to circuit a, is connected directlfy with the journal boxesor wheels of the rontaxle of the vehicle, the inductance of this axleforming part of the inductance of the circuit. The remainder of theapparatus on the vehicle is the same as the apfic conditions in advance,such control may be accom lished by means such as that shown in ig. 3,wherein 31 is a contact arm operativel connected with the. running gearof the vehicle through the mediumof a speed-res onsive device Q so thatthe position of t is arm varies with variations in the speed of thevehicle; the higher the speed, the farther'this arm swings to the right,and vice versa. This arm coiipera tes with fixed-contact segments 32, 33and 34 which are included in circuitswith the contacts of relays P andP". A brake applicationniagnetM is controlledby these circuitsflin thefollowin 'manner. I When both relays and P are energized, the circuitfor magnet M is completed through the upper contact points of} theserelays and-the fixed contact segment 32, which is. of. such length thatthe vehicle may roceed at maximum speed before the circuit will beopenedby the movement of arm 31 be nd the-right hand end" of segment 32.hen, however, relay P becomes deenergized and relay P is energized, thisway and relay R.

being the caution condition of the vehiclecarned apparatus, the circuitfor magnet is completed through upper point of the contact of relay Pand the lower contact point of relay P and segment 33, which segment isshorter than segment 32, so that the vehicle must proceed at anintermediate gized, thebrake pipe remains closed and the.

rakes are not applied. The three speeds corresponding-to segments 32, 33and 34* may be any desired values, such, for example, as '60,. 30 and 10miles per hour.

Referring to Fig.4, I'have here shown diagrammatically the current wave,forms inthe various circuits between the track- Under proceed conditionsthe current in circuitv b is of peril odi'c'alvarying amplitude becauseof the two superimposed currents differing in frequency; if thesecurrents areof equalval'ue. the resultant current will pass through zeroonce for each period as indicated, but, of course, if the two componentcurrents differ in value, the resultant current will not reach 'zero' atany time. The tween filaments 6 and grid cause of the action of thecondenser 23 and resistance 24, and the current in the'primary windingoftransformer 28 will have substantially the same wave formbecause of theactionof the amplifier K". The current in the secondary of transformer28 and in relay R will have the wave form substantially as shown in thethird-line of the diagram,

because of the action of transformer 28. The wave forms under cautionconditions will bereadily understood, "and need not be ex lained indetail. Since. the action of i bu h K in energizing relay R is simply arelaying or amplifying action it is not otential 'be-" i will have,substantially the wave form indicated ber 'thoughtnecessary to explainthe transformations between resonant circuit 5 and relayR by diagram. i

The corresponding circuits on the vehicle have also substantially thesame wave forms as shown in Fig. 4.

Referring now to Fig. 5, I have here shown a system involving anothermeans for producing an oscillating signaling current varyingperiodically in amplitude. G is a generator of low frequency currentsuch .for example as 60 cycles per second, to

which generator are connected transmission mains 38 extending along therallway. Current is supplied to the track rails of each section, andwinding 41of each relay is connected with a secondary 35 of the adjacenttransformer T. Each relay is responsive, therefore, to swing itscontacts 42 and 43 in one direction or the other from the middleposition in accordance with the relative direction of current in thetrack rails-as determined by polechanger N. Each relay S controls afixed or roadside signal F, which,

as here shown, is; of the semaphore type having three ,indicatingpositions. 1 Each signal is controlled by contact 42 of thecorresponding relay in such manner that when the contact is in themiddle osition the signal is inthe horizontal or stop? position; whenthe relay contact swings to the right'it closes a local circuit whichcauses the signal to move to the inclined or caution position; andwhenthe relay contact swings to the left it closes another. local cir-.

cuit which causes the signal toymove to the vertical or proceedposition. The pol,e-- changer N for each block section is controlled bythe signal for the section in advance in the usual manner. The apparatusthus far referred to is old and Well under stood, and needs no furtherexplanation.

Superimposed on the track rails is ahigh frequency current which is usedonly to control the signals or other a paratus on the cars or trains. Asheres own, this high frequency current is furnished by a generator G towhich are connected transmission mains37 extending along the railway.The

0nd. Each block section is supplied with this high frequency currentthrough'a transformer T having an iron core t whose primary is connectedwith the transmission mains 37 through a condenser 45, and whosesecondary is connected with the track rails throu h a condenser 45'. Theprimaryand secondary circuits are preferably tuned to resonanceat thefrequency delivered by generator G. Surrounding a portion of the core tis a coilJ which is connected with the secondary 35 of the adjacenttransformer T whenever contact 4370f the adjacent track relay is swungeither to the right or to the left. The purpose of the coil is toutilize the low frequency current from the transformer T to saturateintermittently the iron core t thus causin periodic variation -inamplitude of the big frequency current admitted to the track rails. Itwill therefore be evident that the current in the mains 37 which is ofasingle frequency is transformed into a current whose am litude variesperiodically, so that the trac rails are supplied with current of highfrequency which possesses a beat. The high frequency and the periodicvariations in amplitude are employed for controlling vehicle-carried:ignals as in the other forms of my invenion.

In order to exclude the high frequenc current from the low freqnencycircuit,

rovide a choke coil'l/ which is connected in the circuit with impedancecoil J and pref-I erably adjacent thereto whereby the passage frequencyfrom the transformer 44 into the track rails. Choke coil L furtherserves to limitthe flow of current from transformer 44 when the trackrails adjacent the transformer are connected together by the wheels of avehicle. I I

In connection with this system, any suitable a paratusmay be arranged un 9; vehicle or responding to the signa ing freuencies in the trackrails, such as that Shown in Fig. 1. Rlelela P on the vehlicle res ndsto the big requency signa in cul i nt and relay P responds to theP61101115! variations in amplitude of the high freuency current. Itshould be here noted t at the periodically varying high frequencycurrent comprises two components of constant amplitude, one of which is'current of a frequency greater than that produced by generator G and theother-of which is a current of a frequency less'than that of G, n

so that if combined, these component currents would produce a beatfrequency of the same I eriodlcity as that produced in the high. equencycurrent from generator G by means of the variable impedance due to coret when the latter is magnetized by low fre fiiiency current in coil J He operation of the system shown in Fig. 5 so far as the vehicle signalsare concerned, will now be readily understood. I

will assume that block section A--B is occupied by a vehicle V which isequip d with the same apparatus as vehicle V in ig. 1. Inasmuch as blocksections A-B and BC are unoccupied except for vehicle V, high frequencycurrent of periodically vary-. ing amplitude is-present in circuit a onthe vehicle, so that both relays P and P are become illuminated. As thevehicle V passes into section DE relay P will also become denergized sothat the stop lamp R will be illuminated.

It will be understood that the circuit'a on vehicle V may be replaced bya circuit a, 'as shown in Fig. 2, and it -will also be understood thatthe speed control a paratus shown in Fig. 3 may be provide on vehicle'veither in conjunction with or as a substitut for the lamps G, Y, and Rshown in Fig. 1. In Fig. 6 I have shown a vehicle carried. apparatuswhich is adapted to be used in conjunction with the track-systems shownin Fig. 1 or 5, and is similar to the apparatus for controlling theroadside signals F shown in Fig. 1 with the exception that the coil 30is employed to reproduce the signaling.current in the circuit 6 insteadof the .primary of the rail bond 3 as in Fig. 1. In-

asmuch as the two apparatuses are identical in construction with theaboveexception, it is thought that a detailed description of Fig. 6 isunnecessary. To avoid confusion the reference characters em loyed in theroadside a paratus of Fig. 1 ave been used in Fig. 6 or designating thecorresponding parts, as will be understood.

The operation of the vehicle-carried apparatus shown in Fig. 6 isidentical with that of the vehicle-carried apparatus shown in Fig. 1,the only dlfierence being, that, initead of employing a single device Kfor energized and the green lamp G is illumi-.

selecting and amplifying the signaling frequencies, two such devicesnamed, one for each of the relays P and. P whereby a more positiveselection and greater amplification of the frequencies may be obtained.

Although I have herein shown and described only certain forms ofsignaling systems and. apparatus embodying my invention, it isunderstood that various changes and modifications may be madethereinwithin the scope of the appended claims without departing from thespirit and scope of my invention.

Having'thus described my invention, whating'means on the vehiclecontrolled by the current in the track rails and res nsive to thevariations in amplitude of 'sa d current but not to said current.

.2. A railway signaling system comprising track rails, means forimpressing thereon two alternating currents difi'ering in freuency, andsignaling means responsiveto t e resulting current of eriodicallyvarying amplitude but not to eit currents alone.

i 3. A railway signaling system comprising er of the signaling avehicle, a receiving circuit thereon, means located in the trackway forimpressing on said circuit two alternating currents difl'ering infrequency, and signaling means on the vehicle controlled by said circuitand responsive to the resulting current therein of periodically varyingamplitude but not to either of the signaling currents alone. 1

- 4. A railway signaling system comprising a vehicle, areceiving circuitthereon, means exterior to the vehicle for impressing on said circuit analternatingcurrent of periodically varyin the ve icle responsive to theperiodic variations of said current but notto said current. 5. A railwaysignaling systemcomprising a vehicle, a receiving clrcult thereon, meansexterior to the vehicle for impressing on said circuit a high frequencyoscillating current,

means. for causing theamplitude'of said current to vary periodically attimes, and sigw naling means on the vehicle selectively responsive tosaid high frequency current and to the perlodlc variat ons of saidcurrent.

v 6. A railway signaling system comprising a track rails, means forimpressing on said rails. alternating current of periodically varyingamlitude, means for detecting the presence 0 said variations, and a slgnalcontrolled by said detecting means.

'7. A railway signaling system comprising track rails, means forimpressing on said rails alternating current of periodicallyvarylast-named current.

amplitude, and signaling means on ing amplitude, meansfor translatingsaid variations into an alternating currentof'the' same frequenc asthatof'the variations, and signalcontrol 'ng means responsive to said 8.A railway signaling system comprising track rails,-means for impressingon said rails alternating currentof periodically yarying amplitude, andsignal-controlling means responslve to the periodic variations "of saidcurrent but not to said current. I

9. A railway signaling system comprisin track rails, means for,impressing on said rails alternating current of periodically varyingamplitude, means for translating said variations'into'an alternatingcurrent of the same frequency as that of the variations, a signalrespons ve to the firstcurrent but not to thesecond andanother signalresponsive to the second currentbutnot to the first.

10. A railway signaling system comprising track rails, means forimpressing on said rails alternating current of periodically varyingamplitude, meansrespons'ive to the presence and absenceofsaidalternating current, other means responsive to the presence andabsence of said variations in amplitude,

and signaling apparatus controlled by said two lastmentioned means. t

11. A railway signalings stem comprising track rails, a track circuil;including said rails and a source of alternating current, a

fixed coilin inductive relation to a portion of said track circuit, arelay located in the trackway, a roadside signal controlled by saidrelay, and an electron amplifier interposed between said coil and saidrelay.

12. A railway signalingsystem comprising track rails, a track circuitincluding said rails and a source of alternating current. a fixed coilin inductive relation to a portion of said track circuit; an electronamplifier located in the trackway and having a heated filament, a plate,and a grid interposed between the two; the terminals of said coil beingconnected with the filament and grid of said amplifier, a plate circuitfor said 1 amplifier comprising a source of direct current and a relay,and a roadside signal con trolled by said relay. a

; 13. A railway signaling system comprising track' rails, atrack'circuit comprising said rails and a source of alternating current,a

trackway circuit receiving a minute amount i of ener from said trackcircuit, arelay located in the trackway, an electron amplitrolled by sairelay.

ing an alternating signaling current on said rails, means controlled bytrafiic conditions in advance for causing the amplitude of said currentto vary periodically, a vehicle, a defierinterposed between saidtrackway circuit and said rela and a roadside signalconvice on thevehicle responsive to the variations in the amplitude of said currentbutin said trackway circuit and responsive to p the variations inamplitude of said current but not to said current itself.

16. Railway trafiic controlling apparatus comprising a trackway circuit,means for constantly supplying alternating signaling current to saidcircuit, means controlled b traflic conditions in advance of saidcircuit for causing the amplitude of said current to vary periodically,a vehicle, a device on the vehicle responsive to the variations in amplitude of said current but not to the cur- ..rent itself, a seconddevice on the vehicle responsive to said current but not tothevariations in amplitude thereof, and

ernin means on said vehicle controlle said evices. 17. Railway trafliccontrolling apparatus comprising a -trackway' circuit, means forimpressing on saidcircuit an alternating current of periodically varyingamplitude, and traffic governing means responsive to periodic variationsin the amplitude of said currentbut not to said current itself.

18. Railway traffic controlling apparatus comprising a trackway circuit,means for supplying an alternating current to said circuit, other meanscontrolled by traffic conditions in advance of said circuit for supply-.mg to said circuit, a second alternating cursupplying to said circuit asecond alternating current differing in frequency from the first therebycausing periodic variations in the amplitude of the first current, avehicle, a device on the vehicle responsive to the variations in theamplitude of the first current but not to the first current itself, asecond device on the vehicle responsive to said first current but not tothe variations in amplitude thereof, and governing means on the vehiclecontrolled by said devices.

20. Railway trafiic controlling apparatus comprising a vehicle, arecelving circuit thereon, means located in the trackway for impressingon said circuit two alternating currents differing in frequency, adevice on the vehicle responsive to the resulting current. ofperiodically varyin amplitude in said circuit but not to eit eralternating current alone, a second device on the vehicle responsive toone of said alternating currents in said circuit but not to theresulting current of periodically varying am litude,

and governing means on the vehic e controlled by said devices.

21. In combination, a section of railway track provided with a trackcircuit, a signal .for sald section, and an electron tube controlled bysaid track circuit for governing said signal and comprising a heatedfilament, a grid and a plate.

22. In combination, a section of railway track. provided with. a trackcircuit, a signal and an electron tube for said section, a rid circuitfor said electron tube-controlle by said track circuit, a plate circuitfor said tube including a source of current, and means associated withsaid plate circuit for controlling said signal.

23. In combination, a section of railway track provided with a trackcircuit; an electron tube having a heated filament, a grid and a plate;a grid circuitfor said tube controlled by said track circuit, a platecircuit for said tube including a source of energy, and a signal forsaid section controlled by said plate circuit.

24. In combination, a section of railway track provided with a trackcircuit, a signal for said section, and means interposed between said,track circuit and said signal for controlling said signal and includingan electron tube having a heated filament, a grid and a plate.

In testimony whereof I affix my signature.

LLOYD V. LEWIS.

